May 30, 2012

New Zealand Reptile Chews Food Unlike Any Other On The Planet

Scientists studying one of New Zealand´s most iconic reptiles have found that it chews its food in a way unlike any other animal on the planet, challenging the popular perception that complex chewing ability is linked to high metabolism.

The tuatara, a beak-headed lizard-like reptile that is the sole living member of a family of reptiles that was widespread during the age of the dinosaurs, is able to slice through its food like a “steak knife” would. Scientists say this could explain how the creature has been able to adapt to the changing world over the past 200 million years.

Using a computer model, the scientists, from University College London (UCL) and the University of Hull, demonstrated how the tuatara chews, raising doubts about the link between chewing and high metabolism in mammals.

“We developed this virtual model using software that is widely used in the analysis of complex engineering systems,” said coauthor Dr Neil Curtis, from University of Hull´s Department of Engineering. “It is the most detailed musculoskeletal model of a skull ever developed and demonstrates the huge potential of this type of computer modeling in biology.”

In the study published in The Anatomical Record, the team of researchers describes how the highly specialized jaws of the tuatara work. When the reptile chews, the lower jaw closes between two rows of upper teeth. Once closed, the lower jaw slides forward a few millimeters to cut food along its sharp teeth, effectively sawing the food apart.

“Some reptiles such as snakes are able to swallow their food whole but many others use repeated bites to break food down. The tuatara also slices up its food, much like a steak knife,” said lead author Dr Marc Jones, UCL Cell and Developmental Biology.

“Because mammals show the most sophisticated form of chewing, chewing has been linked to high metabolism,” explained Jones. “However, the tuatara chews food in a relatively complex way but its metabolism is no higher than that of other reptiles with simpler oral food processing abilities. Therefore the relationship between extensive food processing and high metabolism has perhaps been overstated.”

Due to the shape of the animal´s jaw joint, as the jaws slide forwards they also rotate slightly about their long axes, the team said. This makes shearing very effective and demonstrates that the left and right lower jaws are not fused together at the front as in humans. The specialized jaw function allows for a broader diet.

While the diet of the tuatara includes beetles, spiders, crickets and small lizards, Jones noted that there have been some gruesome discoveries in the reptile´s habitat as well.

“People have described finding seabirds with their heads sawn off,” he told BBC Nature. “Tuatara will tend to go for hatchlings if they can, but as far as I can make out [they] do sometimes take small adults.”

“[We think] they change their diet seasonally - eating lots more seabirds during the summer,” he added.

The study was funded by the Biotechnology and Biological Sciences Research Council (BBSRC) and The Paleontological Association.